The moment also calls for a renewed focus on the so-called Northern Triangle of Central America — the countries of El Salvador, Guatemala and Honduras, which together represent the overwhelming source of migrants crossing our southern border. Unless we address the root causes driving migration from this region, any solutions focused solely on border protection and immigration enforcement will be insufficient.

.. It soon became evident that migration from Central America could not be resolved merely by stronger enforcement at the U.S. border, let alone by building a wall. Instead, we needed to tackle the drivers of migration: crime, violence, corruption and lack of opportunity. We knew the cost of investing in a secure and prosperous Central America was modest compared with the cost of allowing violence and poverty to fester.

Trump has been complaining about her ever since she became head of D.H.S., in December. He didn’t like that she had once served in the Bush Administration, or that Fox News personalities such as Ann Coulter and Lou Dobbs considered her an “open-borders zealot.”

.. Part of Nielsen’s job also involved talking the President down when he floated his own ideas for curbing immigration, many of which he picked up from Fox News. This didn’t endear her to the President, either.

.. two of her most prominent backers from the Bush Administration—Michael Chertoff, a former head of D.H.S., and Frances Townsend, a former homeland-security adviser at the White House—were part of the “Never Trump” movement.

.. Since John Kelly was a retired four-star general who, at the time, enjoyed good standing with the President, disgruntled immigration hard-liners were reluctant to criticize him; they directed their frustration toward Nielsen, instead.

.. The irony is that, since becoming the D.H.S. Secretary, Nielsen has shown herself to be both an extremely tough-minded enforcer of Trump’s immigration agenda and an enthusiastic spokesperson for his Administration.

.. “You can’t be seen as the lapdog of the White House,” one of them said. “That makes the department into a political football.”

.. Nielsen’s embrace of the President’s rhetoric on immigration had politicized the department’s broader mission.

.. While Trump was questioning Nielsen’s place in his Administration this winter and spring, she was forced to try to prove her loyalty.

.. Earlier this month, D.H.S. and the Justice Department announced a new “zero tolerance” policy at the border, vowing to prosecute all unauthorized border crossers, including asylum seekers, for entering the country illegally. One outgrowth of the policy is that parents and their children will be separated once they’re taken into custody. The Administration initially justified its stance by insisting that breaking up families would act as a deterrent, to scare away other families that might try to cross the border

.. “You have to ask yourself,why is she doing what’s she’s doing?” the official told me. “It’s not because she really wants to do it. It’s all posture.”

.. The border wall was another source of contention. Republicans in Congress skimped on funding it in the omnibus bill earlier this year. “That was an insult to the President,” the official said. “And a lot of that is on Nielsen. It was up to her to convince Congress to fund all this.”

.. there is “a cabal of anti-immigration people sprinkled throughout the government. A lot of them used to work for Jeff Sessions, and they all talked.” This group disliked Nielsen, but she survived, in part, because she has had the support of John Kelly.

.. There are additional similarities in how Kelly and Nielsen have handled confrontations with Trump.

.. Kelly, too, has reportedly threatened to resign at times when he couldn’t corral the President.

.. Nielsen does have some leverage. It will be difficult, if not almost impossible, to find a replacement for her—someone who can both appease the President and get confirmed by the Senate.

.. “The Administration can’t get rid of Nielsen. She doesn’t even have a deputy right now to fill in for her if she leaves.”